Agbogidi, O. M., and E. Egho. “Evaluation of Eight Varieties of Cowpea (Vigna Unguiculata (L.) Walp) in Asaba Agro-Ecological Environment, Delta State, Nigeria”. European Journal of Sustainable Development, vol. 1, no. 2, June 2012, p. 303, doi:10.14207/ejsd.2012.v1n2p303.